With the development of display technology, a liquid crystal display (LCD) device has many advantages of high definition, power saving, thin body, and wide application, so it is widely used in a variety of consumer electronic products such as mobile phones, televisions (TV), personal digital assistants, digital cameras, notebook computers, desktop computers etc., and becomes the main stream in the display devices.
Most of the liquid crystal devices in current market are the backlight type liquid crystal display, which includes a liquid crystal display panel and a backlight module. The working principle of the liquid crystal display panel is: placing liquid crystal molecules in two parallel glass substrates, which have many vertical and horizontal fine wires between the two glass substrates; controlling the liquid crystal molecules to change direction by energizing or not energizing; and refracting light of the backlight module to produce frames.
Generally, the liquid crystal display panel is consisting of a color filter (CF) substrate, a thin film transistor (TFT) substrate, liquid crystal (LC) interposed between the CF substrate and the TFT substrate, and a sealant.
In TFT-LCD, vertically aligned (VA) becomes a common mode of large-size TVs, with its advantages of wide viewing angle, high contrast, and no need of friction alignment. The VA techniques are mainly divided into multi-domain vertical alignment (MVA) technique, patterned vertical alignment (PVA) technique, and continuous pinwheel alignment (CPA) technique. Such the VA techniques all are needed to design protrusions or slits on the CF side, at the same time of increasing cost, light transmittance of the display screens are also reduced, to solve a problem of implementing a plane control of the CF side from the point or line control, a new VA display technique, called polymer stabilization vertical alignment (PSVA) technique, is produced.
The greatest feature of polymer stabilization vertical alignment technique is that a polymer layer, which can allow vertical alignment liquid crystal form a pre-inclination angle, is formed on the alignment film. Formation of this polymer film is shown in FIGS. 1A to 1D. As shown in FIG. 1A, a certain ratio of high purity reactive mesogen (RM) 200 is blended in liquid crystal molecules 100. This is a phototropism monomer containing a double bond. As shown in FIG. 1B, before ultraviolet (UV) irradiation, an external voltage is applied to an upper substrate 300 and a lower substrate 100 to allow the liquid crystal molecules generate a pre-inclination angle, and corresponding to different domains, inclination directions of the liquid crystal molecules 100 are different. As shown in FIG. 1C, after the pre-inclination angle is determined with the external voltage, specific UV irradiation is performed, and at this time, the reactive mesogen 200 polymerizes to form a polymer network 500 that attracts the liquid crystal molecules 100 to form a fixed pre-inclination angle. As shown in FIG. 1D, after the UV irradiation is completed and the external voltage is removed, the liquid crystal molecules 100 on surfaces of the upper substrate 300 and the lower substrate 400 still keep at the certain pre-inclination angle.
However, after the reactive mesogen undergoes free radical polymerization under the UV irradiation, there will be more or less reactive mesogen left in the liquid crystal and thus contaminating the liquid crystal, resulting in presence of ghost, and reducing quality of the panel.